Polar Sea Ice

Annotated Teacher Editionhttp://serc.carleton.edu/geomapapp

Purpose In polar regions, when temperatures are cold enough, seawater freezes to form sea ice. In this activity, we investigate the amount of sea ice around the poles, its seasonal variability and its impact on climate change. We also explore the differences between polar regions that result from Antarctica being a continent and the north polar region being an ocean.

Red text provides pointers for the teacher. Each GeoMapApp learning activity is designed with flexibility for curriculum differentiation in mind. Teachers are invited to edit the text as needed, to suit the needs of their particular class.

At the end of this lesson, you should be able to:

Analyze and interpret maps and graphical data. Understand the relationship between incoming solar radiation and temperature. Understand the cause and effect of seasons. Use decades of data to explore climate change.

As you work through GeoMapApp Learning Activities you’ll notice a check box, , and a diamond symbol at the start of many paragraphs and sentences:

Check off the box once you’ve read and understood the content that follows it. Indicates that you must record an answer on your answer sheet.

Equipment required: Calculator.

1. Each polar autumn, temperatures in polar regions become so cold that the surface of the ocean freezes. The area of the polar sea covered by the floating sea ice increases throughout the polar winter. Eventually, warming springtime temperatures cause some of the ice to start melting. This annual freeze-thaw cycle has been studied using satellite data that is stored at the National Snow and Ice Data Center.

1a. On your answer sheet, describe from your own knowledge the difference between the Antarctic and Artic geographical regions. You must use the words “land” and “ocean” in your answer.

Part 1: Antarctica and the Southern Ocean

2. Start GeoMapApp. In the projections window, shown below, click once on the middle map that is circled in the screen shot below. It is the map that shows Antarctica and the Southern Ocean. Then, click the Agree button.

When the map window opens, click on the

button to activate the zoom-in tool and click once on the South Pole at the very centre of the map. That will zoom in on the map so that it looks like this:

The map shows the continent of Antarctica which, by pure coincidence, is today centered upon the South Pole. In the upper left we see the tail of South America.

The map image shows bedrock elevations – the height of the land as if the ice sheet had instantly melted. Shades of greens and browns indicate areas above sea-level, including the high mountains of Antarctica. Shades of white and pink indicate areas where the Antarctic bedrock is below sea-level, pushed down by the weight of the overlying ice. It is important that teachers remind students that green areas on the map of Antarctica do not reflect grassy plains and forests – the green is merely the colour used for a particular range of elevation.

Antarctica is a big continent with an area larger than Europe and almost twice as large as Australia. Much of Antarctica is covered by a thick ice sheet. Brrrr! Its thickest points – about 4,000 m – are about the same height as nine Empire State Buildings stacked on top of each other!The staggering amount of ice that sits on the rocky continent of Antarctica may colour our view of the most southerly continent, making it a barely-conceivable part of planet Earth. From television programs, we may have the impression that Antarctica is some strange frozen, barren place, inhabited by only penguins. In fact, it is a fascinating continent. Even though much of the continent is indeed covered by an ice sheet, there are also tall mountains, volcanoes, like Mount Erebus, and ice-free deserts, such as the remarkable Dry Valleys.

2a. Look at the map on your screen. Lines of latitude and longitude are shown as dashed lines. On your answer sheet, describe the pattern of lines of longitude.The radial lines of longitude lines converge at the pole. A globe, peeled orange or grapefruit can help students understand why the lines of longitude come together at the poles.2b. Now describe the pattern of lines of latitude.Concentric circles that are larger with increasing distance from the pole.

3. In the GeoMapApp menus, go into Basemaps > Regional Maps > Antarctica > Sea Ice Extent (1977-2007) > March Sea Ice Extent. You will see a map that looks like the one to the right. The blue color displayed around Antarctica indicates the area of ocean covered by floating sea ice in the month of March. The image shows the average over a 30-year period of the extent of sea ice in the month of March. A snapshot of, say one or two years’ worth of data may be biased towards short-term anomalies. This 3-decade average, better reflects longer term trends. The image comes from the National Snow and Ice Data Centre (NSIDC).

4. Find the Layer Manager window. If you do not see it, click once on the Layer Manager button. The Layer Manager window should pop up. For the March Sea Ice Extent layer, drag the opacity slider bar to the left and right to alter the transparency of the sea ice map.

4a. On your answer sheet, briefly describe the location and extent of the March sea ice beyond the edge of the continent.The floating sea ice rings the entire continent of Antarctica. Its distribution is asymmetrical. A great extent of sea ice lies in the area between the Antarctic Peninsula and the main land mass, and a thick border is found around the western region. In some eastern areas, the sea ice appears to more closely hug the coastline.

5. In the GeoMapApp menus, go into Basemaps > Regional Maps > Antarctica > Sea Ice Extent (1977-2007) > September Sea Ice Extent. The pale blue color displayed around Antarctica indicates the area covered by floating sea ice in the month of September. Drag the transparency slider bar to the left and right to alter the transparency of the sea ice map layer.

The months of March and September have been chosen because they represent the extremes of the extent of sea ice surrounding Antarctica.In question (5), we aim to have students not only examine the extent of sea ice but to conclude that the extremes occur in seasons that are flipped compared to the seasons we experience in the northern hemisphere. Also, whilst answers to the questions could be distilled to one word or phrase, or even collapsed into a table, the requirement to give written descriptions helps students work on a vital scientific skill.

5a. On your answer sheet, briefly describe the location and extent of the September sea ice.A very wide band of sea ice rings the entire continent of Antarctica. (In the top bar of the GeoMapApp window, the longitude/latitude display shows that the second grid circle from the pole is at 60 degrees S. In September, the sea ice extends to about 60 degrees South- in some places quite a bit more – around much of the continent.)

5b. Using the opacity slider bar to compare the two maps of sea ice extent during March and September, describe similarities and differences of the sea ice extent and note which month is associated with the most sea ice. There is a tremendous difference in sea ice extent between the two months. In the example image shown here, the opacity function has been used to display both months together: the brighter blue is the March extent, the ghost outline in pale blue shows the September extent. March has the least sea ice, September the most. The difference in area of sea ice is quite extraordinary.

GeoMapApp contains sea ice maps for each month. So, to expand the activity, students could systematically load the image for each month and use the transparency function to find relationships. In this activity, we jump to the extremes (the maximum and minimum months) to allow time to explore more aspects of polar sea ice.

5c. State which month you think is colder – March or September. Explain your reasoning based upon your observations of sea ice extent.September, assuming that cold weather produces greater amounts of sea ice. (March is warmest, assuming that warmer weather melts the sea ice that was produced during colder months.)5d. During a typical month of March, New Yorkers are shoveling snow. And, during a typical September they are celebrating Labor Day at the beach. Does this statement about New Yorkers match your observations of Antarctic sea ice?No. The seasonal extremes of sea ice around Antarctica are opposite to the seasons experienced in the US northeast: Antarctica lies at the bottom of the southern hemisphere so the seasons are flipped compared to those in the northern hemisphere.

Part 2: The Arctic region

6. Now let’s turn our attention to the north polar region. Unlike Antarctica, the Arctic region is an ocean surrounded by continents and islands. When viewed from high above the North Pole, looking down, the Arctic Ocean is surrounded by Russia, Norway, Greenland, Canada and Alaska. The map to the right, from Oregon State University, shows those countries.The Arctic may be most familiar to students for two reasons: it is the location of the North Pole, and the home of polar bears.

To study the Arctic region, we’ll look at some graphical data.

7. Graph A on the next page shows the amount of floating Arctic sea ice throughout the year. Months are given along the x-axis and the area covered by sea ice is on the y-axis. The graph is a compilation of data from the International Arctic Research Centre and the Japanese space exploration agency, JAXA.This graph contains a lot of useful information. It is a graphical representation of the same type of imagery data that was used earlier in this activity for the Antarctic sea ice extent. There are seven separate curves plotted on the same axes and we will use the graph later to investigate the change of sea ice over years and decades.

7a. Choose any one of the solid or dashed curves. On your answer sheet, describe the general appearance of the curve and note which month is associated with the most sea ice and which month is associated with the smallest amount of sea ice.Students may need help focusing upon just one curve. Since all of the curves display the same overall characteristics it does not matter which curve is chosen. Student answers should note that the greatest extent of Arctic sea ice occurs in northern hemisphere spring time, around March, with the minimum area covered by sea ice being at the end of summer, in September. The area of sea ice changes fairly smoothly throughout the year (the graphs have an overall sinusoidal-like property), and the amount of ice changes by a factor of about 2 - 3 times, depending upon which graph was chosen. For example, during the 2000s decade, sea ice tended to change from a minimum area during autumn of about 5.5 million sq. km to a springtime maximum of around 14 million sq. km.

Graph A

7b. Using your answers from questions (7a) and (5b), write the names of the months in the spaces in the table on your answer sheet.Students have now examined sea ice for both polar regions using different types of data (geospatial imagery and graphical data) and have identified the months containing the maximum and minimum extents of sea ice. When they fill in the table, shown here, they will immediately see that the two regions exhibit opposite sea ice extent properties. The maximum extent in the northern hemisphere corresponds to the minimum extent in the southern hemisphere and vice versa.

Region Month with Maximum area of sea ice

Month with Minimum area of sea ice

Antarctic ( = south polar region) September MarchArctic (= north polar region) March September

7c. Using your knowledge of the winter and summer solstices, explain the relationship between the timing of the solstices and the times of maximum and minimum sea ice extent. (Hint: the term “lag” may be helpful to you here.)We might expect that the coldest time in the Arctic is around the northern hemisphere winter solstice and, therefore, that the maximum sea ice extent will also occur around that time. But, our observations reveal, perhaps surprisingly, that the maximum sea ice extent is actually quite close to the spring equinox. Similarly, the minimum sea ice extent would probably be expected to coincide with the northern hemisphere summer solstice but, in fact, occurs close to the vernal equinox. The opposite is true for Antarctic sea ice since southern hemisphere seasons are reversed

compared to the northern hemisphere seasons. The lag between the solstices and the extremes of ice extent is the key concept here.

8. Graph B displays two data sets on one graph. The brown curve shows the average amount of incoming solar radiation (also called “insolation”) received throughout one year at a high northerly latitude – for an area of the Beaufort Sea that lies above the Arctic Circle, north of Alaska. The black curve shows the average air temperature at the same location.

Graph B

This image is from the National Snow and Ice Data Centre. (URL for image: http://nsidc.org/arcticmet/factors/temperature.html). Averaged air temperature, in dark blue, corresponds to the Y-axis on the left. Incoming solar radiation, in brown, is read off from the Y-axis on the right. The term “Global Radiation” is the sum of all radiation sources received at the ground for any particular locality. It includes the direct radiation from the sun and solar radiation that has been refracted in the atmosphere.

8a. Using Graph B, determine and record the month and amount of maximum incoming radiation. Be sure to include the units.About 370 W/m2 in June. On the graph, 12 data points are used to plot the curve. Each point is the average value for that particular month and is plotted on the graph at the start of each month. For example, let’s consider June. The maximum length of day – and thus, the maximum incoming

solar radiation for one day – would be on the summer solstice of about 21st June, the monthly average is plotted on the graph at the start of June. If daily data points had been used, it would be easier to see the solstices.8b. List the months for which the value of Global Radiation equals zero.Approximately November, December, January.8c. Remember that the graphical data is for a location north of the Arctic Circle. Explain why the amount of solar radiation is zero for some months of each year.Since the Beaufort Sea lies above the Arctic Circle, no sun is visible for a span of time that is centred upon the northern hemisphere winter solstice. The monthly averages used in the graph indicate that all of December and some parts of January and November fall in darkness. It’s important that your students understand that the only location in the northern hemisphere that experiences a full six months of darkness is the north pole, and that the duration of the total darkness decreases southward.

8d. From the graph, determine and record the three highest values of Air Temperature, and the months in which they occur. What are the units?About 1-3oC, in June, July and August (see note in (8a) about the plotting of monthly averages).

8e. Also from the graph, determine and record the three lowest values of Air Temperature, and the months in which they occur. Be sure to include the units.Approximately -26 oC, -27 oC and -25 oC in January, February and March. Those are mind-numbing minus temperatures!8f. Describe the relationship between the time of maximum incoming solar radiation and the time of maximum air temperature. Then, describe the relationship between the time of minimum incoming solar radiation and time of minimum air temperature. (Hint: the term “lag” may again be useful to you here.)There is a lag in the maximum daily temperature in the north polar region compared to the time at which the northern hemisphere experiences maximum incoming solar radiation. Similarly, there is a lag between the winter solstice and the months that experience the minimum temperatures.

8g. Explain possible causes for the relationships you described in (8f).Polewards of the tropics, we always see the lag between maximum incoming solar radiation and maximum temperature and between minimum insolation and minimum temperature. Our graph is for a location in the Beaufort Sea. The graph shows that, around the summer solstice, the sun is visible in the Beaufort Sea 24 hours a day – the midnight sun. The long warming periods of sunlight warm the ground and air. In July and August when the sun briefly dips below the horizon at night time, those short nights provide very little time for surface cooling, and there remains more energy absorbed during the day than is lost at night. Overall, maximum average summer temperatures typically lag one to two months after the maximum sun elevation. The maximum temperature is reached when the outgoing, night-time radiation finally equals the incoming daytime radiation (when the two are in equilibrium). For winter, the same type of reasoning can be applied – during the long winter nights, more energy is radiated away from Earth than is gained during the short days. For a period of time after the winter solstice, temperatures continue to drop until, finally, the incoming daytime radiation increases enough to be in equilibrium with the outgoing night-time radiation.

An additional important factor for polar regions is the influence of albedo which can have a significant effect upon temperature: Areas covered by snow and ice reflect much incoming solar radiation but land and ocean areas absorb the radiation. But, for this exercise, we do not go into that amount of albedo detail.

(Similarly, all over Earth, the lowest temperature of the day generally occurs not in the middle of the night, but in the moments before sunrise, following a night of coolling. And, maximum daytime temperature generally falls behind maximum (solar noon) insolation due to the time delay in the heating of the ground. After solar noon, the sun gets lower in the sky but insolation exceeds outgoing terrestrial radiation until they briefly come into equilibrium which marks the maximum temperature.)

9a. Summary of changes in annual sea ice Using non-technical terms, write one paragraph that ties together our observations of Antarctic and Arctic sea ice extent with our interpretations of solar radiation and air temperature data.From solar radiation and air temperature data, we learnt that the minimum and maximum air temperatures lag the solstices. The period of lowest air temperature coincides with the times for which we observe the most sea ice coverage, which makes sense. The period of highest air temperature coincides with the times for which we observe the least amount sea ice coverage. The north and south polar regions are in opposite hemispheres and the period of least sea ice coverage in one polar region corresponds to the time of most sea ice in the other hemisphere.

Part 3: The world’s changing climate

10. The analysis of data collected over lengthy time periods helps us identify long-term trends.

Look once more at Graph A. The curves show the amount of Arctic floating sea ice that has been recorded in the north polar region over the last three decades. Carefully study the maximum and minimum values shown by the separate curves.

At the maximum values, around March, the curves are closely spaced. So, on average over the last 30 years, the maximum amount of sea ice that re-forms each wintertime is about the same. From the scale on the Y-axis, we see that maximum area covered by sea ice is about 14 million square km.

10a. Now look carefully at the minimum values, around September. Use the scale on the left side of the graph to find the area covered by sea ice for the 1980s, 2000s and 2012 and fill in the values in the table on your answer sheet.

Time period Area in millions of square km

1980s 7.3

2000s 5.6

2012 3.5

10b. For the year 2012, the maximum area covered by sea ice is about 14.5 million sq. km. Using your value for 2012 minimum sea ice extent (from question (10a)), calculate the percentage of ice that melted during the summer months in 2012. Show your work.The area covered by sea ice at the end of summer = 3.5 million sq. km. So, about 14.5 – 3.5 = 11 million sq. km. of sea ice melted during the summer. As a percentage, that melted ice value is given by (11 / 14.5 ) * 100 = 76%. That is a staggering figure and represents the most melting since scientific records began.

10c. Based upon the trends you see Graph B, do you expect the summertime coverage of sea ice in the north polar area in the year 2030 to be more than, the same as or less than the area covered in 2012? (Circle one phrase on your answer sheet.)

10d. Researchers link the increasingly widespread melting of Arctic sea ice during summer months to the world’s warming climate. The globe has been warming for at least the last century. With what you have heard or read about global warming and Earth’s changing climate, briefly explain the relationship between fossil fuels and global warming, and suggest two ways that the effects of global warming may be slowed.There is uncontestable evidence that the burning of fossil fuels and the resultant release into the atmosphere of combustion gases such as CO2 is causing the planet’s temperature to rise through the Greenhouse Effect. Suggestions for slowing global warming include reducing the amount of fossil fuel usage; switching to greener forms of energy generation that wind, solar and wave action; and, reducing the amount of methane, a very potent greenhouse gas, that comes, for example, from the decomposition of organic matter in landfills. Note, however, that due to residency time of greenhouse gases in the atmosphere, global temperatures will continue to rise for decades to come, even if we could today magically stop the emission of all excess human-derived greenhouse gases.

OPTIONAL WORK:

The activity so far has focussed upon data for one year periods. We can also examine changes in Arctic sea ice over recent decades. The graph in question 7 displays seven separate curves for the extent of Arctic sea ice: Curves averaged over each of three decades (1980s, 1990s, 2000s) and curves for four specific years (2007, 2008, 2011, and 2012). The teacher could have students use the data in that graph to explore longer-term trends (example: the amount of summer Arctic sea ice in 2012 was about half of what it was just 30 years ago) and couple that with an examination of news reports about the alarming rate of summer ice melting, potential effects upon the flow of ocean currents, links with climate change and effect upon shipping. Examples of relevant news stories are here:

Impact of record low measurements:http://www.bbc.co.uk/news/science-environment-19652329http://www.economist.com/node/21563278Video animation, shipping routes, oil and gas exploration: http://www.economist.com/blogs/dailychart/2011/09/melting-arctic-sea-ice-and-shipping-routeshttp://www.economist.com/node/21556798http://www.bbc.co.uk/news/science-environment-20454757

The NSIDC graph at right could also be used to examine long-term trends in Arctic summer ice extent. Teachers could, for example, use an image editor to erase the blue trend line and have students determine the trend.

Ties with Arctic ecology (e.g. the fate of polar bears) could also be incorporated.

URL for information on 1979-2012 Arctic sea ice extent graph:http://nsidc.org/arcticseaicenews/2012/10/poles-apart-a-record-breaking-summer-and-winter/ And download link for high-resolution image:http://nsidc.org/arcticseaicenews/files/2000/09/Figure3.png

A note: Unlike the Arctic, the recent extent of Antarctic sea ice area is slightly above average and is thought to be a result of recent strong circumpolar winds that help push sea ice outwards which slightly increases the area covered.

Required prior knowledge: Knowledge of the seasons and solstices. Ability to read and interpret maps and graphs.

Short Summary of concepts and content: The relationship between polar sea ice and seasons. Comparison of map-based and graphical data sets to find relationships. Implications of climate change.

Description of data sets: The various data sets used in this activity originate from the National Snow and Ice Data Centre. (URL: http://nsidc.org/)